This invention relates generally to medical probes used for contracting soft tissue, and more particularly, to medical probes for shrinking damaged collagen tissue by applying heat.
Medical probes for the rehabilitative heat treatment of damaged soft tissues are known in the art. Examples of these probes include laser probes and RF heated probes. While these tools meet the basic need for rehabilitative heat treatment of soft tissues, such as collagen tissues, many suffer from temperature over-shoot and under-shoot causing unpredictable results in the heating of soft tissue.
Soft tissue is the most abundant tissue in the human body. Most soft tissue is collagenxe2x80x94over 90% of the organic matter in tendon, ligament, and bone is collagen. The connective tissue in joints is soft tissue, generally collagen tissue. When soft tissue in a joint is damaged, the healing process is often long and painful.
Well known treatments for addressing soft tissue damage in joints include strengthening exercises, open surgery, and arthroscopic techniques. Using current treatments, many people with injured joints suffer from prolonged pain, loss of motion, nerve injury, and some develop osteoarthritis. The soft tissue in many injured joints never heals enough to return the damaged joint to its full function.
It is known in the art that non-ablative thermal energy applied to unstable soft tissue, such as collagen tissue, in joints may alter or manipulate the tissue""s healing response. In particular, applying controlled thermal energy to damaged soft tissue in a joint can cause the collagenous tissue to shrink, thereby tightening unstable joints.
Medical probes employing heat for the thermal manipulation of soft tissue are known in the art. For example, U.S. Pat. No. 5,458,596 to Lax, et al., discloses examples of a probe with a proximal and distal end that employs heat for the controlled contraction of soft tissue. However, a potential drawback of many prior art probes is that the probe""s temperature can become unstable when heat from the probe is dissipated into the mass of the treated tissue. This situation can be a particular problem when treating dense tissue; dense tissue acts as a heat sink thereby requiring additional energy input to maintain the desired temperature. The application of additional energy in an attempt to compensate for the heat sink effect can cause an underdamped effect before settling out at the correct temperature.
In general, a system is underdamped when its damping factor is less than 1. A system is critically damped when its damping factor is exactly 1. And, a system is overdamped when its damping factor is greater than 1. Curve A in FIG. 6 illustrates a typical time-temperature response curve for an underdamped prior art heat application probe. The underdamping shown in curve A results from a system with a very small damping factorxe2x80x94for example, a damping factor less than 0.5.
The xe2x80x9cringingxe2x80x9d shown in curve A is a problem because it can cause the momentary application of temperatures that are too high for the safe heating of soft tissue. When this occurs, the soft tissue may be further damaged by being charred or ablated. One reason for the difficulties of prior art probes in providing smooth and consistent heating is that preferred materials for the energy delivery electrodes are highly thermally responsive materials. Such materials generally do not store large amounts of heat energy so that overshoot at initiation (from rapid heating to achieve operating temperature) and underdamped fluctuations during application (often from contact with large tissue masses) present control difficulties.
There is, therefore, a need in the art for an inexpensive and disposable instrument for heating soft tissues that maintains greater control and more constant temperature while initiating and applying treatment.
Based on the foregoing, an object of the invention is to provide a tissue heating probe that will maintain a more constant temperature while initiating and applying thermal applications to targeted soft tissues.
This and other objects are achieved according to the present invention by a medical instrument that includes an elongated body portion with a proximal and distal end and two cooperative heating sources. The first heating source is preferably disposed on the distal end of the elongated body. In the preferred embodiment, the first heating source is an RF electrode. The second heating source is preferably disposed proximally behind the first heating source and provides secondary heat to the first heating source. The first heating source is chosen to provide a more rapid thermal response than the second heating source. The second heating source is chosen such that it has a higher heat capacity than the first heating source, such that the temperature fluctuations in the first heating source are dampened or compensated for by the second heating source.